1. Field of the Invention
The present invention relates generally to water heaters or boilers and, more specifically, to a method of manufacturing a modular vertical tube tank for such a water heater or boiler which can be coated for corrosion protection prior to assembly.
2. Description of the Prior Art
Water heaters and boilers (referred to collectively as water heaters in the discussion which follows) typically have a water heater tank, often of the vertical tube type which utilizes fire tubes located above a combustion chamber. Vertical shell or V-shell heat exchangers of the above type are well known in the industry. In these water heaters, a fossil fuel power burner may be used in the combustion chamber. The products of combustion from the combustion chamber pass vertically upward through the open interiors of the vertical tubes and out a flue outlet.
In the past, the vertical tube sheet and surrounding shell were an integral unit. A head was welded on each of the initially open ends of the generally cylindrical shell, each head having a plurality of aligned apertures. A plurality of vertical tubes were then inserted into the aligned apertures and welded into place.
In order to provide potable water, it was generally necessary to line the interior of the shell and the exterior of the vertical tubes with a corrosion inhibitor. For instance, the fire tubes could be clad on the water side with pure copper sheathing. Another coating used in the industry is electroless nickel which is a nonferrous, corrosion resistant shield. In certain of the prior art processes, the interior of the shell and the water side of the fire tubes were coated by a slush coating process in which the coating was applied through an opening such as the water inlet or outlet in the shell with the unit being rotated or agitated until the coating had uniformly distributed itself.
One problem with the prior art coating technique was that it was not possible to adequately inspect the inside of the slush coated water heater tank since the only openings into the previously welded tank were of relatively small diameter and the tank heads and vertical tubes had been welded into place. Another problem with slush coating was that such coatings typically had volatile organics which exceeded currently allowable VOC emission standards under applicable EPA guidelines.
The present invention has as its object to provide an improved vertical tube tank for a vertical shell and tube heat exchanger of the type used in water heater and boiler design.
Another object of the invention is to provide a vertical tube tank for a water heater having a tank and tube sheet of modular design.
Another object of the invention is to provide a manufacturing method for such a water heater which allows visual inspection of the corrosion resistant coating prior to assembly of the modular components into the completed device.
Another object of the invention is to provide a manufacturing method for such a water heater which allows the components of the shell and tube sheet to be coated by an electrostatic coating process, thereby obviating the need for slush coating techniques with high VOC emissions.